The interest in electrochemical conversion of solar to chemical energy has encouraged an increase in research to find inexpensive, high-performing, and stable reduction-oxidation (redox) catalysts. In particular, significant attention has been given to transition-metal-based oxides to catalyze the highly complex four-electron oxidation of water to molecular oxygen.
The kinetics of oxygen evolution show the following trend in catalytic activity: RuO2>IrO2>Co≈Ni containing oxides >Fe≈Mn≈Pb containing oxides. Remarkably, this trend is almost completely the reverse of their abundance in the Earth's crust: Fe(56.3 g/kg)>Mn(0.95 g/kg)>Ni(0.08 g/kg)>Co(0.03 g/kg)>Pb(0.01 g/kg)>Ir, Ru(10−6 g/kg). It is thus highly desirable to find forms of the more abundant elements that would be comparable to, if not surpass, the Ir or Ru-containing compounds. Ti is one of the most abundant transition metals in the Earth's crust (5.65 g/kg), but Ti oxides suffer from very low electrocatalytic oxygen evolving activity.
The (110) surface termination of TiO2 (rutile) is a poor oxygen evolving catalyst due to its weak oxygen binding energy. Other rutile-type structures such as IrO2 and RuO2 are found to be more effective catalysts, due in part to the much more flexible oxidation states of their metal ions. However, in addition to composition, catalyst structure is another fundamental determinant of catalytic reactivity.
SrTiO3 is known to decompose water into H2 and O2 upon illumination with light. However due to its high band gap energy (3.2 eV), its application is limited to UV irradiation, the same as TiO2-rutile.
Most studies concerning SrTiO3 as water decomposition catalyst has been therefore concentrated on precious metal doping of SrTiO3 for it to absorb in the visible light region. None have ventured on the study on the efficacy of the SrTiO3 surface as a site of reaction. It has been shown that TiO2-rutile is a poor surface catalyst for O2 production, its oxygen evolving activity stems from the fact that under intense irradiation with UV light, the over potential associated with the evolution of O2 is compensated. Accordingly, there is a need in the art for designing a water decomposition system not only concerning band gap engineering but also surface reactivity modifications.